Interaction of Nck1 and PERK phosphorylated at Y561 negatively modulates PERK activity and PERK regulation of Pancreatic β-cell Proinsulin Content.

PERK, the PKR-like endoplasmic reticulum (ER) kinase, is an ER transmembrane serine/threonine protein kinase activated during ER stress. In this study, we provide evidence that the Src-homology domain-containing adaptor Nck1 negatively regulates PERK. We show that Nck directly binds to phosphorylated Y561 in the PERK juxtamembrane domain through its SH2 domain. We demonstrate that mutation of Y561 to a non-phosphorylatable residue (Y561F) promotes PERK activity, suggesting that PERK phosphorylation at Y561 (pY561PERK) negatively regulates PERK. In agreement, we show that pY561PERK delays PERK activation and signaling during ER stress. Compatible with a role for PERK in pancreatic β-cells, we provide strong evidence that Nck1 contributes to PERK regulation of pancreatic β-cell proteostasis. In fact, we demonstrated that down-regulation of Nck1 in mouse insulinoma MIN6 cells results in faster dephosphorylation of pY561PERK, which correlates with enhanced PERK activation, increased insulin biosynthesis and PERK-dependent increase in proinsulin content. Furthermore, we report that pancreatic islets in whole body Nck1 knockout mice contain more insulin than control littermates. Altogether, our data strongly suggest that Nck1 negatively regulates PERK by interacting with PERK and protecting PERK from being dephosphorylated at its inhibitory site pY561, and in this way impacts pancreatic β-cell proinsulin biogenesis.